P4 cost is about right, penetration buff at vet? You already have excellent AT in the stug. The P4 should not be a one stop shop, it should be an intermediate answer to everything?
The problem is you can't afford a PIV and a StuG III, the PIV locks you into having a unit putzing around that doesn't scale well when facing off against heavies/advanced tanks like the ISU/IS2/Churchill variants/Comet/Easy Eight/T34/85 because it's pen is sub par for what your paying for.
Basically a lot of the issue lay in Ostheer T3 being very expensive, and the USF 75mm low velocity Sherman having the exact same pen for lower cost on it's AP shells with the added bonus of the ability to switch to HE shells that are great for wiping low model count Ostheer squads right off the map.
The solution lay in two things; either making the PIV better in pen or something else or lowering it's cost. It was suggested in the other thread putting the Ost one at 115 and OKW at 125.
Volks have quite a bit of versatility right now. Buffing their AI would limit the importance of other units and make them a one stop shop again. If you want AI use Sturms, then elite infantry and obers. AI upgrade is hard to understand because then volks would be able to deal with their counters. Volks are vulnerable to AI units because they should be.
But no other army in the game has to make this sacrifice. Conscripts get AT nades, molotovs, better veterancy, and doctrinally they get an AI upgrade. USF can put basically anything on it's mainline infantry (and doctrinally add the ability to put down Schu mines). Brits can also put any variety of upgrades they want on their mainline infantry as well.
Simply put, Volks are the only basic infantry in the game with neither a doctrinal upgrade or a selection of upgrades period. This of course isn't getting into the fact Volks scaling got a huge kick in the nuts with the Conscript and Rifle scaling buffs.